[DOC] add animation of right sidebar

Author: SimonBlanke

docs/source/_static/css/custom.css

@@ -138,9 +138,21 @@ html[data-theme="dark"] {
     border-left: none;
 }
 
-/* Fixed position for right sidebar */
+/* Right sidebar slide-in animation on page load */
+@keyframes slideInFromLeft {
+    from {
+        opacity: 0;
+        transform: translateX(-20px);
+    }
+    to {
+        opacity: 1;
+        transform: translateX(0);
+    }
+}
+
 .bd-sidebar-secondary {
     min-width: 200px;
+    animation: slideInFromLeft 0.3s ease forwards;
 }
 
 .pst-page-navigation-heading {